Development of Face Recognition Entails Brain Tissue Growth

Approximately 2% of the adult population is poor at recognizing faces, a disorder
sometimes referred to as facial blindness. Brain regions that recognize faces have a unique cellular make-up, suggested a new study.

Development of Face Recognition Entails Brain Tissue Growth

The work overturns a central thought in neuroscience, which is that
the amount of brain tissue goes in one direction throughout our lives -
from too much to just enough. The group made this finding by looking at
the brains of an often-overlooked participant pool: children.

‘Brain regions that recognize faces have a unique cellular make-up. The microscopic structures within the region change from childhood into adulthood over a timescale that mirrors improvements in people's ability to recognize faces.’

People are born with brains riddled with excess neural connections.
Those are slowly pruned back until early childhood when, scientists
thought, the brain's structure becomes relatively stable. Now a pair of studies, published in Science and Cerebral Cortex,
suggest this process is more complicated than previously thought. For
the first time, the research group found microscopic tissue growth in the brain
continues in regions that also show changes in function.

"I would say it's only in the last 10 years that psychologists
started looking at children's brains," said Kalanit Grill-Spector, a
professor of psychology at Stanford and senior author of both papers.
"The issue is, kids are not miniature adults and their brains show that.
Our lab studies children because there's still a lot of very basic
knowledge to be learned about the developing brain in that age range."

Grill-Spector and her team examined a region of the brain that distinguishes faces from other objects. In Science,
they find that the microscopic structures within the region change from
childhood into adulthood over a timescale that mirrors improvements in
people's ability to recognize faces.

"We actually saw that tissue is proliferating," said Jesse Gomez,
graduate student in the Grill-Spector lab and lead author of the Science
paper. "Many people assume a pessimistic view of brain tissue: that
tissue is lost slowly as you get older. We saw the opposite - that
whatever is left after pruning in infancy can be used to grow."

Microscopic brain changes

The group studied regions of the brain that recognize faces and
places, respectively, because knowing who you are looking at and where
you are is important for everyday function. In adults, these parts of
the brain are close neighbors, but with some visible structural
differences.

"If you could walk across an adult brain and you were to look down
at the cells, it would be like walking through different neighborhoods,"
Gomez said. "The cells look different. They're organized differently."

Curious about the deeper cellular structures not visible by magnetic
resonance imaging (MRI), the Stanford group collaborated with
colleagues in the Institute of Neuroscience and Medicine, Research
Centre Jülich, in Germany, who obtained thin tissue slices of
post-mortem brains.

Over the span of a year, this international
collaboration figured out how to match brain regions identified with
functional MRI in living brains with the corresponding brain slices.
This allowed them to extract the microscopic cellular structure of the
areas they scanned with functional MRI, which is not yet possible to do
in living subjects. The microscopic images showed visible differences in
the cellular structure between face and place regions.

"There's been this pipe dream in the field that we will one day be
able to measure cellular architecture in living humans' brains and this
shows that we're making progress," said Kevin Weiner, a Stanford social
science research associate, co-author of the Science paper and co-lead author of the Cerebral Cortex paper with Michael Barnett, a former research assistant in the lab.

Neighborhoods of the brain

This work established that the two parts of the brain look different
in adults, but Grill-Spector has been curious about these areas in
brains of children, particularly because the skills associated with the
face region improve through adolescence. To further investigate how
development of these skills relates to brain development, the
researchers used a new type of imaging technique.

They scanned 22 children (ages five to 12) and 25 adults (ages 22 to
28) using two types of MRI, one that indirectly measures brain activity
(functional MRI) and one that measures the proportion of tissue to water
in the brain (quantitative MRI). This scan has been used to show
changes in the fatty insulation surrounding the long neuronal wires
connecting brain regions over a person's lifetime, but this study is the
first to use this method to directly assess changes in the cells'
bodies.

What they found, published in Science, is that, in addition
to seeing a difference in brain activity in these two regions, the
quantitative MRI showed that a certain tissue in the face region grows
with development. Ultimately, this development contributes to the tissue
differences between face and place regions in adults. What's more,
tissue properties were linked with functional changes in both brain
activity and face recognition ability, which they evaluated separately.
There is no indication yet of which change causes the other or if they
happen in tandem.

A test bed

Being able to identify familiar faces and places, while clearly an
important skillset, may seem like an odd choice for study. The reason
these regions are worth some special attention, said Grill-Spector, is
because we can identify them in each person's brain, even a five-year-old
child, which means research on these regions can include large pools of
participants and produce results that are easy to compare across
studies.

What's more, the fusiform gyrus, an anatomical structure in the
brain that contains face-processing regions, is only found in humans and
great apes (gorillas, chimps, bonobos and orangutans).

"If you had told me five or 10 years ago that we'd be able to
actually measure tissue growth in vivo, I wouldn't have believed it,"
Grill-Spector said. "It shows there are actual changes to the tissue
that are happening throughout your development. I think this is
fantastic."

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